Materials or preparations suitable for use as pressure-sensitive adhesives have permanent tackiness, good ability to flow onto different surfaces, and a balanced amount of adhesion and cohesion. Typically, foliar materials are preferentially coated with pressure-sensitive adhesives, so that the end-user enjoys the convenience of a self-adhesive product such as adhesive tape, stick-on labels or the like. For the preparation of such self-adhesive products the pressure-sensitive adhesive preparation must be applied in liquid form to the particular substrate and then be solified by suitable measures. The simplest and oldest method of doing this is to dissolve the adhesive in organic solvents. Large amounts of solvents, however, require either the burning off of the solvent vapors from the drying operation, or the use of a recovery system. These costs and disadvantages are avoided by the use of aqueous adhesive dispersions, yet the drying of aqueous preparations requires a high energy input and permits only low manufacturing speeds.
Pressure-sensitive adhesives which have to be applied in the molten state are, for example, products on the basis of block copolymers of styrene and isoprene or butadiene, as they are first described in U.S. Pat. No. 3,229,478. Melt adhesives of this kind, however, require high temperatures of over 150.degree. C., for example, in order to be sufficiently fluid for the coating operation. Furthermore, the material has poor stability against atmospheric oxygen, heat and light, and against solvents. Thus, it cannot be used in critical, high-performance applications.
There has been no lack of attempts to produce a pressure-sensitive adhesive by chemical reaction from fluid polymer mixtures. The use of polyesters as a basis for pressure-sensitive adhesives in a reactive system is described in German Federal Patent No. 32 20 865, according to which a reaction of hydroxyl polyesters with alkoxysilyl-functional compounds produces crosslinkable polymers, but even at 100.degree. C. they set too slowly.
All these reactive systems have numerous difficulties in common: the difficulty of precisely proportioning the functionalizing compounds, their insufficient speed of reaction, and especially the inconsistency of the properties of the pressure-sensitive adhesive. There are difficulties in all reactive systems in achieving the balance between the adhesive strength and cohesive strength of the adhesive. Often post-reactions occur when the self-adhesive product is stored, which can result in great changes in their properties and even in a loss of tack.
In the other fields of printing inks and protective coatings there is the curing of polyesters containing (meth)acrylic groups of high-energy radiation, i.e., ultraviolet light or electron beams (EB) according to DE-OS No. 28 38 691 and DE-OS No. 34 21 826, and the direct radiation-induced polymerization of monomeric mixtures according to U.S. Pat. No. 3,772,063, as well as the hardenable solution of polymers or prepolymers in monomer mixtures according to U.S. Pat. No. 4,133,731. Disadvantages in fabrication are high contents of still-unbound esters of (meth)acrylic acid, producing inflammable vapors which are toxic and irritate the mucous membranes and have a very offensive odor. Even after polymerization or crosslinking, there is still an unacceptably high content of residual monomers to be found.
Radiation-setting melt adhesives according to U.S. Pat. Nos. 4,052,527 and 4,438,177 can be processed only at high temperatures, require high radiation dosages to set them, resulting in damage to the substrate, and they provide too little variability in the properties of the adhesive.
The problem therefore existed of developing pressure-sensitive adhesives having the following properties:
free of solvents and other volatile components, PA0 free of unsaturated monomers, low odor, nontoxic, PA0 free as possible of color, preferably water-clear, PA0 applicable at low temperatures of no more than 50.degree. to 120.degree. C., PA0 curable at low radiation energy of, e.g., 2 to 5 Mrad, PA0 high production rate in coating operation, even when applying large amounts of adhesive, PA0 coverage of a broad range of adhesive properties, including the high performance range of high strength and low aging by light, oxygen or heat. PA0 (a) Base polyesters are used containing hydroxyl groups and having average molecular weights of 1,000 to 10,000 and being fluid at 20.degree. C., from the group: PA0 wherein 10 to 90% of the hydroxyl groups of the polyesters according to a are reacted with acrylate compounds or methacrylate compounds, PA0 (b) the acrylate compounds or methacrylate compounds being selected from the group of: PA0 (c) the polyesters bearing methacrylic groups or acrylic groups thus prepared are spread as a thin coating to the surface of substances and crosslinked or set by means of electron beams or ultraviolet radiation, optionally after the addition of a photoinitiator with the formation of permanently tacky surfaces of the pressure sensitive adhesive layers. PA0 (b) in a second step, reaction of 10 to 90% of the hydroxyl groups of the polyester with acrylic compounds or methacrylic compounds from the group: PA0 (c) polyesters bearing methacrylate groups or acrylate groups are applied in a thin coating and crosslinked by electron beams or ultraviolet radiation thereby forming pressure-sensitive adhesives having permanently tacky surfaces. PA0 as tri- and polyfunctional polycarboxylic acids: trimellitic acid, trimesinic acid, hemimellitic acid, pyromellitic acid and their polyester-forming derivatives, and very preferentially trimellitic acid anhydride and trimellitic acid monoalkyl ester, dialkyl ester and trialkyl ester; PA0 as dicarboxylic acids: e.g., terephthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid, isophthalic acid, phthalic acid and aliphatic dicarboxylic acids with 2 to 12 carbon atoms, as well as their polyester-forming derivatives such as azelaic acid, sebacic acid and dodecanic acid; PA0 as triols and polyfunctional polyols: glycerol, pentaerythritol and, very preferentially, trimethylolpropane, trimethylolethane, di-trimethylolpropane ethers and their esters and ethers, glycidyl esters of monocarboxylic acids, especially the so-called versatic acids; PA0 as mono- or dihydroxycarboxylic acid: e.g., hydroxysuccinic acid (malic acid) and, as diols, aliphatic diols with 2 to 6 carbon atoms such as monoethylene glycol or hexanediol, as well as ether diols such as diethylene glycol, triethylene glycol and on up to polyether glycols with molecular weights of 1,000.
This problem is solved by the invention.